You can easily localize where the gravity originates and how strong it is. That part is easy as long as you are moving and can measure course changes as you move.

Then you look in that direction and see what you can see. If you see nothing then it's not a star. So either a planet or a black hole.

Either way, avoid it.

For that matter, avoid it if it's a star. It's a general rule: if it gravitates avoid it.